Why do we keep talking about appropriate sample sizes for usability tests? Perhaps the most important factor is the economics of usability testing. For many practitioners, usability tests are fairly expensive events, with much of the expense in the variable cost of the number of participants observed (which includes cost of participants, cost of observers, cost of lab, and limited time to obtain data to provide to developers in a timely fashion). Excessive sampling is always wasteful of resources , but when the cost of an additional sample (in usability testing, an additional participant) is high, it is very…
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